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Synop&c and Orographic Control of Observed Drop Size Distribu&ons (DSDs) during the OLYMPEX Field
Campaign
Joe Zagrodnik Lynn McMurdie, Robert A. Houze
University of Washington—Department of Atmospheric Sciences
17th Conference on Mountain Meteorology
28 July 2016
NASA grants: NNX13AG71G, NNX15AL38G, and NNX16AD75G NSF grant: AGS-‐1503155
OLYMPEX Precipita&on Totals
Seed Orchard
CRN Site 540m
280m
1020m 85m
10 km
Quinault HW x
180m 115m
640m
65m
375m
Graves Creek
375m
Nov 12-‐13: Widespread extreme rainfall totals
Highest totals (>300 mm) at lower-‐eleva&on sites near Lake Quinault Up to 4 &mes more than the coast!
Rain Shadow
175-‐275 mm farther up Quinault Valley and in Wynoochee high terrain
Nov 13 0600 UTC 500 hPa Height (contours), Vor&city (colors)
L
H
850 hPa Temp(colors), Height (contours)
“Westerly Atmospheric River”
NPOL Sounding 0600 UTC 13-‐Nov
45 kt wind at 925 hPa
Nov 12-‐13 Rain rates
~18 hour period of orographic enhancement
More rain at low-‐eleva&on CRN site compared with interior/higher eleva&on sites
Max orographic enhancement
Weaker bright band
No data (power outage)
Near-‐surface dBZ remains constant
“Pre-‐warm frontal”
“Warm Sector”
Big drops falling fast
Orographic enhancement associated with large quan&&es of < 1.5 mm drops
Max orographic enhancement
These small-‐medium sized drops are responsible for the majority of the increase in rain rate
Time (UTC)
Rain Rate (m
m/h)
Diam
eter (m
m)
Drop
s per m
3 mm
-‐1
Drop
Diameter bin (m
m)
CRN
NPOL RHI 13-‐Nov 02:12 UTC 50° Azimuth
NPOL
Reflec&vity
Velocity
Low-‐level jet is within 1 km of the surface near NPOL and starts liping around 20 km from radar (white arrow). Drop forma&on + growth occurs below mel&ng level ahead of high terrain. Jet liping decreases 50-‐60 km from radar.
Graves
NPOL
Quinault HW
Mountain
10-‐13 UTC, medium-‐to-‐large sized drops account for the increase in rain rate!
Max orographic enhancement SNOW
SNOW
DOW RHI 13-‐Nov
02:04 UTC 65° Azimuth
DOW RHI 13-‐Nov
11:14 UTC 65° Azimuth
Graves
DOW
Quinault HW
Enhancement later in event at Quinault HW possibly related to evolu&on of low to mid level jet. Appreciable shear is observed between upper and lower layers.
Weaker low-‐level flow
Deeper, stronger jet
Reflec&vity Velocity
CRN
Summary of Nov 12-‐13 Case: • Impressive rainfall totals came from predominately warm orographic enhancement (rapid growth and fallout of small rain drops).
• Warm enhancement processes dominated: – Within the warm sector of this AR event – During the period of highest rain rates (at CRN) – At rela&vely low eleva&ons – When the low-‐level jet lips below the mel&ng level
• Cold precipita&on was also present throughout the event (evidenced by a bright band). One period of likely cold enhancement (at Quinault HW) when LLJ was the strongest and near/above the bright band.